Deposition apparatus and method for forming a pyrolytic graphite article



June 23, 1964 R. J. DIEFENDORF DEPOSITION APPARATUS AND METHOD FOR FORMING A PYROLTIC GRAPHITE ARTICLE Filed June 26. 1961 MI. A d w 4 Q m 2 \1 WM? 5 pfl i 7 A QM i4 wfw u an R vvvvvvv u United States Patent 3,138,435 DEPOSITION APPARATUS AND METHOD FOR FDRMING A PYRQLYTIC GRAPHITE ARTICLE Russell J. Dielendorf, Schenectady, N.Y., assignor to General Eiectric Company, a corporation of New York Filed June 26, 1961, Ser. No. 119,538 14 (Jlaims. (Cl. 23209.1)

This invention relates to apparatus and methods of forming articles and more particularly to apparatus and methods of forming pyrolytic graphite articles.

This application is a continuation-in-part'of my copending application filed December 12, 1960, as Serial Number 75,244, now abandoned. I

Pyrolytic graphite is defined as a material made from carbonaceous gases by thermal decomposition or from a carbonaceous material by evaporation and deposition on a surface. In pyrolytic graphite, planar graphite crystallites are arranged so that their layer structures are parallel .to the deposition surface. It is useful as a high temperature material for lamp filaments, furnace linings and neutron reactor moderators. Development of missile and space propulsion systems has created an additional requirement for pyrolytic graphite components in these systems.

carbonaceous gases have been thermally decomposed and deposited on a surface to produce pyrolytic graphite. As a result of the decomposition, carbon .is removed from the gas and deposits on the surface so that planar graphite crystallites are aligned into a layer structure. It is desirable to provide pyrolytic graphite articles at high deposition rates which articles have similar properties. Since high deposition rates are desirable, it would appear that only the gas pressure need be increased in the deposition chamber to produce a corresponding increase in deposition rate. However, a uniform deposition at an increased rate depends upon a number of variables, such as chamber diameter, surface distance from gas flow,

gas pressure, pressure drop, temperature, geometry of proposed article and carbon contentof the gas flow. Thus, a mere increase in pressure does not solve the deposition problem but imposes a subsequent limitation by creating generally soot which produces a material with poorer physical properties. Therefore, it would be desirable to provide a deposition apparatus and methods of forming pyrolytic graphite without soot particles at an increased rate of deposition.

It is an object of my invention to provide an improved deposition apparatus for forming pyrolytic graphite articles. L

It is another object of my invention to provide a deposition method of forming pyrolytic graphite articles.

It is a further object of my invention to provide a deposition method of forming pyrolytic graphite articles of uniform thickness, having similar properties, and at high rates of deposition. I

In carrying out my invention in one form, a deposition method comprises providing an enclosure, positioning a member within the enclosure and spaced therefrom to provide a narrow passagetherebetween, evacuating said passage, and flowing a carbon vapor ata temperature in the range of 2000 C. to 2500 C. through the passage whereby pyrolytic graphite is formed on the member and the enclosure.

These and various other objects, features, andv advantages of the invention will be better understood from the following description taken in connection with the accompanying drawing in which:

FIGURE 1 is a sectional view of a deposition apparatus embodying my invention; and

FIGURE 2 is a sectional view of a modified enclosure,

gas, can be used with cyanogen.

3,138,435 Patented June 23, 1964 chimney and member which is also employed in the deposition apparatus of FIGURE 1.

In FIGURE 1, a deposition apparatus is shown generally at 10 which comprises a chamber 11 having a lower body portion12 and a cover 13 which is hinged to the'lower body portion by means of bolts 14 and employs an 6 ring 15 therebetween. Viewing window 16 is provided in cover portion 13 to view the operation and to read an optical pyrometer (not shown). A preheater 17 is positioned on the inner surface of the bottom wall of chamber 11 and consists of a container 18 having an inlet 19 and outlet 20. A baflle 21 is positioned within the preheater and is provided with a plurality of openings 22 around the perimeter thereof.

A feed line 23 is connected at the inlet opening 19 of preheater 17 and extends through the bottom Wall of chamber 12 to a carbonaceous material source (not shown). A carbonaceous gas is fed from the source through a meter 24 showing the total consumption of gas, a gas rate meter 25, an acetone and Dry Ice trap indicated at 26, and line 23 to preheater 17. While a pure carbonaceous gas, such as methane, ethane, propane, acetylene, benzene, carbon tetrachloride, or cyanogen, is employed, the carbonaceous material can also be in liquid or solid form which is fed from the source to preheater for conversion to a carbon vapor. I found further that such a carbonaceous gas can be mixed with a non-carbonaceous gas which reacts with the carbonaceous gas during its decomposition to carbon. For example, hydrogen, as the reacting gas, can be employed with the alkanes or alkynes while nitrogen, as the reacting An enclosure 27 of graphite or other high temperature material having an inlet 28 and an outlet 29 is positioned on preheater 17 by aligning inlet 28 of the enclosure with outlet 20 of preheater 17. Enclosure 27 can beconstructed of several pieces, such as alower portion3'0 and an upper portion 31 joined together. In this manner, a member 32 is placed within the enclosure and sup. ported therein in a relatively simplefashion. There is shown a member 32 of graphite or other high tempera-v ture material supported concentrically within enclosure 27 by means of pins 33 which extend through the mem-' ber 32 and through the walls of, enclosure 2'7. Addition ally, nuts 34 have been applied on the pins 33 adjacent to the exterior surface of mandrel 32 tohold the mandrel in position within'enclosure '27. I found also that the use'of reentrant angles on the mandrel allows the pyro-' lytic graphite article formed thereon to be easily sepa rated from the mandrel. Member 32 and enclosure 27f form a narrow passage 35 between the exteriorsurface}. of member 32 and the interior surface of enclosure 27. I prefer toemploy a uniform diameter passage or a pas sage narrowing toward its outlet to produce a more. uni- J forxndeposition. A chimney 36 surrounds outlet .29 of enclosure 27 to provide for removal of fumes whichipass';

through passage 35 between member32 and the interior wall of enclosure 27. Suitable insulation in the form of carbon black 37 surrounds enclosure 27 and is held in.

position by a, quartz or asbestos paper cylinder 38. Con- 43 is shown which has an inlet 44 and outlet 45'. A chimney 46 is positioned across outlet 45 and is provided with a plurality of apertures 4'7 to provide for removal of fumes. A rod 48 with a threaded end 49 extends downwardly to support a member 50 by means of a threaded portion 51. Member 50 and enclosure 43 form a narrow passage 52 therebetween. Enclosure 43 is positioned on preheater 17 within chamber 11 of deposition apparatus 10, shown in FIGURE 1.

While it is disclosed in FIGURES l and 2 that the enclosure is a oneor two-piece structure, a plurality of pieces can be employed so that the interior surface of the enclosure can be machined to conform to the exterior contour of the mandrel. Additionally, the chimney can be supported from the interior wall of lower body portion 12 or cover 13. If desired, the mandrel support can be extended through the enclosure inlet.

I discovered unexpectedly that pyrolytic graphite articles were deposited uniformly and without soot particles at high volume carbonaceous gas flow rates by positioning concentrically a member within an enclosure, spacing the member from the enclosure to provide a narrow passage therebetween, evacuating the passage and flowing a carbon vapor at a temperature in the range of 2000 C. to 2500" C. through the passage. I found further that a fixed diameter passage should have a diameter of at least twice the deposition thickness since both the member and enclosure wall are coated in the process. The passage diameter is also determined by the member diameter and passage length to provide a negligible pressure drop. The concentration gradient of carbon to be deposited should also be small.

It appears that the soot particle is probably formed by the growth of a large carbon molecule which upon reaching a critical size is coated around its periphery with smaller aromatic molecules. These smaller molecules are oriented with their basal planes parallel to the surface of the larger molecule. If a large diameter chamber is employed at low pressure, the large carbon molecule does not have time to diffuse to the chamber wall before it forms soot. If a small diameter chamber is used at low pressure, the large carbon molecule does have time to diffuse to the chamber wall. However, a mere in crease in pressure in the small diameter chamber to increase deposition produces generally soot with a resulting less desirable deposited material. Addition of hydrogen has been employed to inhibit the growth of the large carbon molecules.

In the operation of deposition apparatus 10 shown in FIGURE 1, a member 32 is positioned concentrically within upper body portion 31 by means of bolts 33 and nuts 34. Portion 31 is athxed to lower body portion 30 to form enclosure 27. Member 32 and enclosure 27 are spaced apart to provide a narrow, substantially uniform diameter passage therebetween. Since the narrow passage diameter will be fixed, it is determined by the member diameter and passage length to provide a negligible pressure drop and by a requirement for a diameter at least twice the thickness of the proposed member deposition. Enclosure 27 is then positioned on preheater 17 with outlet 20 of preheater 17 and inlet 28 of enclosure 27 in alignment. Chimney 36 is placed over outlet 29. Cylinder 38 surrounds enclosure 27 and provides a space which is filled with carbon black insulation. An induction coil 39 surrounds cylinder 38 for heating preheater 17, enclosure 27, member 32, and passage 35. Cover 13 is bolted to lower body portion 12 of chamber 11.

The chamber atmosphere is reduced preferably to the lowest obtainable vacuum. Power is supplied to induction coil 39 which heats preheater 17, enclosure 27, member 32, and passage 35 to a temperature of at least 2350 C. to purify member 32 and the interior wall of enclosure 27. During heating, the pressure rises while upon completion, the pressure falls to its initial value. This heating step removes from iron and other impurities, which boil to the surfaces of the member and enclosure, and ad sorbed gases which are present. I have found that the employment of this heating step provides member 32 with a surface on which fine-grained pyrolytic graphite is formed. The power is then shut off and the assembly within chamber 11 is allowed to cool. I prefer generally to bring the chamber to atmospheric pressure and open the chamber to inspect the mandrel and enclosure prior to forming pyrolytic graphite articles. Any carbon black present on the surfaces is removed manually. It is not necessary to shut ofi the power, cool the assembly, open and inspect the chamber since a carbon vapor can be flowed through the enclosure passage subsequent to the purification of the deposition surface to form pyrolytic graphite. After such an inspection, cover 13 is bolted again to lower body portion 12, and chamber 11 atmosphere is reduced preferably to the lowest obtainable vacuum.

A carbonaceous gas, such as methane, is fed through a total consumption meter 24, a gas rate meter 25, and an acetone and Dry Ice trap 26 prior to entering preheater 17 through gas line 23. Power is supplied to induction coil 39 to bring the temperature of preheater 17, enclosure 27, member 32 and passage 35 up to a temperature in the range of 2000 C. to 2500 C. I have found that this temperature range is desirable to produce uniform pyrolytic graphite articles with a density of approximately 2.2 gm./cm. Such density is desirable to provide a freestanding body which can be removed readily from the member. The carbonaceous gas is preheated in preheater 17 at a temperature in the above temperature range whereby a carbon vapor is formed. If a liquid or solid carbonaceous material is used, the material is fed to preheater 17 in which it is converted to its gaseous form and then to a carbon vapor.

While I prefer to use induction coil 39 to heat preheater 17, enclosure 27, member 32, and passage 35, the carbonaceous gas can be preheated from a separate heat source to the desired temperature to provide a carbon vapor which flows through passage 35. Additionally, the carbonaceous gas can be fed to passage 35 where heat is supplied to enclosure 27, member 32, and passage 35 to decompose the gas to a carbon vapor. However, I have found it most desirable to preheat the gas in preheater 17 and feed the carbon vapor through passage 35 while enclosure 27, member 32, and passage 35 are heated to maintain the temperature of the vapor in the passage. Although some of the carbon vapor deposits on the walls of the preheater, most of the vapor is deposited on the enclosure and the member. I have found also that the most beneficial results are secured from employing additionally a narrow, uniform diameter passage or a passage narrowing toward its outlet. The pre-heating step and uniform or tapering passage tend to maintain a uniform coating thickness.

The above process with a carbonaceous gas can be carried out over a wide range of flow conditions, such as 0.5 mm. to 760 mm. of mercury, at various gas flow rates, such as 20 to cubic feet per hour which is similar to molecular flow. The addition of a reacting gas, such as hydrogen, with the carbonaceous gas creates a flow condition which is similar to molecular flow in that the reacting gas slows down growth of the carbon particles to provide more time for diffusion to the wall prior to attaining critical size for soot formation. Generally, a ratio of at least one to one of reacting gas to carbonaceous gas is employed. In the course of my research on uniform deposition at an increased rate which disclosed that such deposition depends upon a number of variables which were mentioned above, I have found, also unexpectedly, that the highest rate of deposition occurs immediately prior to a sooting environment. Accordingly, the car bon vapor flow rate is increased to produce a sooting environment which is observed through window 16 in cover 13 of the apparatus. Thereafter, the vapor flow is reduced below sooting environment and the flow continued to form pyrolytic graphite on the member and enclosure. After the desired thickness of the pyrolytic graphite article is attained, the gas flow is stopped, the pressure is decreased further, and the assembly within chamber 11 is allowed to cool to room temperature. The pressure is increased subsequently to atmospheric pressure, and cover 13 is removed to provide access to enclosure 27.

Portion 31 is detached from portion 30, and mandrel 32 removed from portion 31. With the particular type of member 32 employed in FIGURE 1, the coated member is cut in two or the article is cut at approximately its midpoint to remove the pyrolytic graphite articles therefrom. Additionally, reentrant angles can be employed to provide for easy separation of the article from the member. I found also that the member can be constructed of several pieces and include a partial central bore which causes the member to collapse upon removal of the article. During the operation of forming such articles, the temperature is recorded by an optical pyrometer (not shown) which is viewed through window 16 in cover 13.

Temperatures in the range of 2000 C. to 2500 C. can be employed to produce articles on member 32. At such temperatures, it is possible to form 20 to 40 mils of pyrolytic graphite an hour to produce articles having a wall thickness of 100 to 200 mils without soot inclusions.

If it is desired to provide a thicker deposition on a portion of member 32, the member can be eccentrically positioned within enclosure 27. In this manner, a pyrolytic graphite article can be formed with a wall of varying thickness. 1

In FIGURE 2 of the drawing, there is shown a modified enclosure 43 with an inlet 44, and outlet 45. A chimney 45 with a plurality of openings 47 is supported on the upper end of enclosure 43 across outlet 45. Chimney 46 has a rod 4% extending downwardly within enclosure 43 which terminates in a threaded end 49. A member 50 is-supported within enclosure 43 by means of plurality of threads 51 which mate with threads 49 of rod 4%. Enclosure 43 and member 50 provide a uniform diameter passage 52 therebetween.

In operation, modified enclosure 43 with member 50 thereon is positioned in apparatus of FIGURE 1 by seating enclosure 43 on preheater 17. Inlet 44 of enclosure 43 and outlet of preheater 17 are in alignment. A pyrolytic graphite article is formed on member 50 in the same manner as described above for forming an article on member 32. I

Additionally, pyrolytic graphite sheets are formed in a similar manner by employing members in sheet form. A plurality of these sheets are positioned within an enclosure and spaced apart to provide a passage between adjacent pairs of sheets. A passage can also be provided between the enclosure and the members. Pyrolytic graphite is formed on these sheets in the same manner as described above for'forming an article on member 32. The pyrolytic graphite article is subsequently removed from each of the sheet members. I

Several examples of methods of forming pyrolytic graphite articles in accordance with the present invention are as follows:

" Example I A deposition apparatus was set up generally in accordance with FIGURE 1 of the drawing wherein both the enclosure and the member were composed of commercial graphite to, form an annular passage which narrowed from inch to /2 inch toward the outlet. The member which included reentrant angles, a removable bottom portion, and a central bore, had a maximum diameter of 2% inches, and a length of 4 /2 inches. After the cover was bolted to, the lower body portion, the chamber atmosphere was reduced to a pressure of .001 mm. of mercury by the pump. Power was supplied to the induction coil to heat the member, enclosure, and passage to an uncorrected optical pyrometer temperature reading of about 2285 C. During heating the pressure rose. After repressure fell. The power was discontinued, and the deposition apparatus was allowed to cool to room tempera ture. The chamber was then opened, inspected, and closed. The chamber atmosphere was again reduced to a pressure of .001 mm.of mercury. Power was supplied to the induction coil to heat the enclosure, member, passage, and preheater to an uncorrected optical pyrometer temperature reading of 2285 C. A carbonaceous gas in the form of methane was supplied at a rate of 36 cubic feet per hour at a pressure of 1140 mm. of mercury to the preheater subsequent to flowing through metering devices, and an acetone and Dry Ice bath. The gas formed into a carbon vapor in the preheater which was deposited uniformly on both the member and interior enclosure wall as it flowed through the narrow passage at a pressure of approximately 18 mm. of mercury. After five hours, the power and gas flow were discontinued and the chamber was restored to atmospheric pressure. room temperature, the member was removed from the enclosure. The pyrolytic graphite article was removed from the member. The article had a thickness of 180 mils.

Example II A deposition apparatus was set up generally in accordance with FIGURE 1 of the drawing wherein both the enclosure and the member were composed of commercial graphite to form an annular passage which narrowed from inch to /2 inch toward the outlet. The member, which included reentrant angles, a removable bottornportion, and a central bore, hada maximum diameter of 2% inches, and a length of 4%. inches. After the cover was bolted to the lower body portion, the chamber atmosphere was reduced to a pressure of .001 mm. of mercury. Power was supplied to the induction coil to heat the member, enclosure, and passage to an uncorrected optical pyrometer temperature reading of about 2285 C. Dur- After removal of iron,

ing heating the pressure rose. other impurities and adsorbed gases, the pressure fell. The power was discontinued, and the deposition appara tus was allowed to cool to room. temperature. The chamber was then opened, inspected, and closed. The chamber atmosphere was again reduced to a pressure of .001 mm. of mercury. Power was supplied to the induction coil to heat the enclosure, member, passage, and preheater to an uncorrected opitcal pyrometer temperature reading of 2285 C. A carbonaceous gas in the form of methane was supplied to the preheater subsequent to flowing through metering devices, and an acetone and Dry Ice bath to form a carbon vapor. The carbon vapor flow was increased to 38' cubic feet per hour to produce a sooting environment which was viewed through the cover window. The flow was then reduced to 36 cubic feet per hour which was below the sooting environment. The

carbon vapor was deposited on both the member and in terior enclosure wall as it flowed through the passage at a pressure of approximately 18 mm. of mercury. After five hours, the power and gas flow were discontinued and the chamber was restored to atmospheric pressure. After cooling to room temperature, the member was removed The pyrolytic graphite article'was from the enclosure. removed from the member. The article had a thickness of 180 mils.

Example III mercial graphite. A passage was provided between each pair of sheets. The sheets were positioned so that each passage narrowed from 3 inches width to 1 inchwidth toward the enclosure outlet. After the cover was bolted to the lower body portion, the chamber atmosphere was reduced to a pressure of .020 mm. of mercury by the pump. Power was supplied to the induction coil to heat After cooling to the sheets, enclosure, and passages to an uncorrected optical pyrometer temperature reading of about 2130 C. During heating the pressure rose. After removal of iron, other impurities and adsorbed gases, the pressure fell. The power was discontinued, and the deposition apparatus was allowed to cool to room temperature. The chamber was then opened, inspected, and closed. The chamber atmosphere was again reduced to a pressure of .020 mm. of mercury. Power was supplied to the induction coil to heat the enclosure, members, passage, and preheater to an uncorrected optical pyrometer temperature reading of 2150 C. A mixture of a carbonaceous gas in the form of methane and hydrogen gas at a ratio of one to one parts was supplied at a rate of 60 cubic feet per hour at a pressure of 1140 mm. of mercury to the preheater subsequent to flowing through metering devices, and an acetone and Dry Ice bath. The gas formed into a carbon vapor in the preheater which was deposited on the sheets as it flowed through the passage at a pressure of approximately 6 mm. of mercury. After 85 hours, the power and gas flow were discontinued and the chamber was restored to atmospheric pressure. After cooling to room temperature, the sheets were removed from the enclosure. The pyrolytic graphite article was removed from each sheet and had a thickness of 500 mils.

Example IV A deposition apparatus was set up generally in accordance with FIGURE 1 of the drawing. Three sheets of commercial graphite having dimensions of 6 inches by 7 inches were spaced apart within an enclosure of commercial graphite. A passage was provided between each pair of sheets. The sheets were positioned so that each passage narrowed from 1 inch width to /1 inch width toward the enclosure outlet. After the cover was bolted to the lower body portion, the chamber atmosphere was reduced to a pressure of .001 mm. of mercury by the pump. Power was supplied to the induction coil to heat the sheets, enclosure, and passages to an uncorrected optical pyrometer temperature reading of about 2250 C. During heating the pressure rose. After removal of iron, other impurities and adsorbed gases, the pressure fell. The power was discontinued, and the deposition apparatus was allowed to cool to room temperature. The chamber was then opened, inspected, and closed. The chamber atmosphere was again reduced to a pressure of .001 mm. of mercury. Power was supplied to the induction coil to heat the sheets, members, passages, and preheater to an uncorrected optical pyrometer temperature reading of 2300 C. A carbonaceous gas in the form of methane was supplied at a rate of 33.0 cubic feet per hour at a pressure of 1140 mm. of mercury to the preheated subsequent to flowing through metering devices, and an acetone and Dry Ice bath. The gas formed into a carbon vapor in the preheater which was deposited on the sheets as it flowed through the passages at a pressure of approximately 18 mm. of mercury. After three hours, the power and gas flow were discontinued and the chamber was restored to atmospheric pressure. After cooling to room temperature, thee sheets were removed from the enclosure. The pyrolytic graphite article was removed from each sheet and had a thickness of 70 mils.

Example V A deposition apparatus was set up generally in accordance with FIGURE 1 of the drawing. Three sheets of commercial graphite having dimensions of 3% inches by 4 inches were spaced apart within an enclosure of commercial graphite. A passage was provided between each pair of sheets. The sheets were positioned uniformly so that each passage was inch wide. After the cover was bolted to the lower body portion, the chamber atmosphere was reduced to a pressure of .001 mm. of mercury by the pump. Power was supplied to the induction coil to heat the sheets, enclosure, and passages to an uncorrected optical pyrometer temperature reading of about 2250 C. During heating the pressure rose. After removal of iron, other impurities and adsorbed gases, the pressure fell. The power was discontinued, and the deposition apparatus was allowed to cool to room temperature. The chamber was then opened, inspected, and closed, The chamber atmosphere was again reduced to a pressure of .001 mm. of mercury. Power was supplied to the induction coil to heat the sheets, members, passages, and preheater to an uncorrected optical pyrometer temperature reading of 2280 C. A carbonaceous gas in the form of methane was supplied at a rate of 150 cubic feet per hour at a pressure of 1140 mm. of mercury to the preheater subsequent to flowing through metering devices, and an acetone and Dry Ice bath. The gas formed into a carbon vapor in the preheater which was deposited on both the sheets as it flowed through the passages at a pressure of 20 mm. of mercury. After 3 hours, the power and gas flow were discontinued and the chamber was restored to atmospheric pressure. After cooling to room temperature, the sheets were removed from the enclosure. The pyrolytic graphite article was removed from each sheet and had a thickness of mils.

While other modifications of this invention and variations of method which may be employed within the scope of the invention have not been described, the invention is intended to include such that may be embraced within the following claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A deposition method which comprises providing an enclosure, positioning a member within said enclosure, providing a narrow, substantially uniform diameter passage between said member and said enclosure thereby providing a negligible pressure drop during deposition, evacuating said passage, flowing a carbon vapor at a temperature in the range of 2000 C. to 2500 C. through said passage whereby a pyrolytic graphite article is formed on said member, and removing said article from said member.

2. A deposition method which comprises providing an enclosure, positioning a member within said enclosure, providing a narrow, substantially uniform diameter passage between said member and said enclosure thereby providing a negligible pressure drop during deposition, evacuating said passage, flowing a mixture of a carbon vapor and hydrogen at a temperature in the range of 2000 C. to 2500 C. through said passage whereby a pyrolytic graphite article is formed on said member, and removing said article from said member.

3. A deposition method which comprises providing an enclosure, positioning a member within said enclosure, providing a narrow, substantially uniform diameter passage between said member and said enclosure thereby pro viding a negligible pressure drop during deposition, evacuating said passage, heating said member and said enclosure to a temperature in the range of 2000 C. to 2500 C., flowing a carbon vapor through said passage whereby a pyrolytic graphite article is formed on said member, and removing said article from said member.

4. A deposition method which comprises providing an enclosure, positioning a member within said enclosure, providing a narrow, substantially uniform diameter passage between said member and said enclosure thereby providing a negligible pressure drop during deposition, evacuating said passage, feeding a carbonaceous material to' said enclosure, preheating said material to decompose said material to a carbon vapor, and flowing said carbon vapor at a temperature in the range of 2000 C. to 2500 0., through said passage whereby a pyrolytic graphite article is formed on said member, and removing said article from said member.

5. A deposition method which comprises providing an enclosure, positioning a member within said enclosure, providing a narrow, substantially uniform diameter passage between said member and said enclosure thereby proarsaaas viding a negligible pressure drop during deposition, evacuating said passage, feeding a carbonaceous material to sald enclosure, preheating said material to decompose said material to a carbon vapor, heating said member, and said enclosure to a temperature in the range of 2000 C. to 2500 C., flowing said carbon vapor through said passage whereby a pyrolytic graphite article is formed on said member, and removing said article from said member.

6. A deposition method which comprises providing an enclosure, positioning a member within said enclosure, providing a narrow, substantially uniform diameter passage between said member and said enclosure thereby providing a negligible pressure drop during deposition, evacuating said passage, flowing a carbon vapor at a temperature in the range of 2000" C. to 2500 C, through said passage, increasing said flow to produce a sooting environment, reducing said flow below said sooting environment, and continuing said flow whereby a pyrolytic graphite article is formed on said member, and removing said article from said member.

7. A deposition method which comprises providing an enclosure, positioning a member within said enclosure, providing a narrow, substantially uniform diameter passage between said member and said enclosure thereby providing a negligible pressure drop during deposition, evacuating said passage, heating said member and said enclosure to a temperature in the range of 2000 C. to 2500 C., flowing a carbon vapor through said passage, increasing said flow to produce a sooting environment, reducing said flow below said sooting environment, and continuing said flow whereby a pyrolytic graphite article is formed on said member, and removing said article from said member.

8. A deposition method which comprises providing an enclosure, positioning a member within said enclosure, providing a narrow, substantially uniform diameter passage between said member and said enclosure thereby providing a negligible pressure drop during deposition, evacuating said passage, feeding a carbonaceous material to said enclosure, preheating said material to decompose said material to a carbon vapor, flowing said carbon vapor at a temperature in the range of 2000 C. to 2500 C. through said passage, increasing said flow to produce a sooting environment, reducing said flow below said sooting environment, and continuing said flow whereby a pyrolytic graphite article is formed on said member, and removing said article from said member.

9. A deposition method which comprises providing an enclosure, positioning a member within said enclosure, providing a narrow, substantially uniform diameter passage between said member and said enclosure thereby providing a negligible pressure drop during deposition, evacuating said passage, feeding a carbonaceous material to said enclosure, preheating said material to decompose said material to a carbon vapor, heating said member and said enclosure to a temperature in the range of 2000 C. to 2500 C., flowing said carbon vapor through said passage, increasing said flow to produce a sooting environment, reducing said flow below said sooting environment, and continuing said flow whereby a pyrolytic graphite article is formed on said member, and removing said article from said member.

10. A deposition method which comprises providing an enclosure, positioning a plurality of members within said enclosure, providing a narrow passage between said members and said enclosure, providing a narrow passage between each pair of adjacent members, evacuating said passages and flowing a carbon vapor at a temperature in the range of 2000 C. to 2500 C. through said passages whereby pyrolytic graphite articles are formed on said members, and removing said articles from said members.

11. A deposition method which comprises providing an enclosure, positioning a plurality of members within said enclosure, providing a narrow passage between said members and said enclosure, providing a narrow passage between each pair of adjacent members, evacuating said passages, flowing a carbon vapor at a temperature in the range of 2000 C. to 2500 C. through said passages, increasing said flow to produce a sooting environment, reducing said flow below sooting environment, and continuing said flow whereby pyrolytic graphite articles are formed on said members, and removing said articles from said members.

12. A deposition method which comprises providing an enclosure, positioning a plurality of members within said enclosure, providing a narrow passage between each pair of adjacent members, evacuating said passages, and flowing a carbon vapor at a temperature in the range of 2000- C. to 2500 C. through said passages whereby pyrolytic graphite articles are formed on said members, and removing said articles from said members.

13. A deposition method which comprises providing an enclosure, positioning a plurality of members within said enclosure, providing a narrow passage between each pair of adjacent members, evacuating said passages, flowing a carbon vapor at a temperature in the range of 2000 C. to 2500 C. through said passages, increasing said flow to produce a sooting environment, reducing said flow below sooting environment, and continuing said flow whereby pyrolytic graphite articles are formed on said members, and removing said articles from said members,

14. A deposition apparatus comprising a chamber, a preheater having an inlet and outlet positioned in said chamber, carbonaceous material feed means connected to the inlet of said preheater, an enclosure having an inlet and an outlet supported on said preheater, said enclosure inlet communicating with the outlet of said preheater, a member positioned witrin said enclosure, said enclosure and said member spaced apart to provide a narrow, substantially uniform diameter passage therebetween, said enclosure outlet communicating with said chamber, an insulated cylinder surrounding and spaced from said enclosure and said preheater, insulation surrounding said enclosure and said preheater within said cylinder, heating means surrounding said cylinder, and means for maintaining a pressure in said passage.

References Cited in the file of this patent UNITED STATES PATENTS 494,150 De Lodyguine Mar. 28, 1883 1,352,086 Rose Sept, 7, 1920 2,002,003 Eisenhut et a1 May 21, 1935 2,261,319 Wilcox Nov. 4, 1941 2,405,449 Robinson Aug. 6, 1946 2,487,581 Palumbo Nov. 8, 1949 2,763,581 Freedman Sept. 18, 1956 

1. A DEPOSITION METHOD WHICH COMPRISES PROVIDING AN ENCLOSURE, POSITIONING A MEMBER WITHIN SAID ENCLOSURE, PROVIDING A NARROW, SUBSTANTIALLY UNIFORM DIAMETER PASSAGE BETWEEN SAID MEMBER AND SAID ENCLOSURE THEREBY PROVIDING A NEGLIGIBLE PRESSURE DROP DURING DEPOSITION, EVACUATING SAID PASSAGE, FLOWING A CARBON VAPOR AT A TEMPERATURE IN THE RANGE OF 2000*C. TO 2500*C. THROUGH SAID PASSAGE WHEREBY A PYROLYTIC GRAPHITE ARTICLE IS FORMED ON SAID MEMBER, AND REMOVING SAID ARTICLE FROM SAID MEMBER.
 14. A DEPOSITION APPARATUS COMPRISING A CHAMBER, A PREHEATER HAVING A INLET AND OUTLET POSITIONED IN SAID CHAMBER, CARBONACEOUS MATERIAL FEED MEANS CONNECTED TO THE INLET OF SAID PREHEATER, AN ENCLOSURE HAVING AN INLET AND AN OUTLET SUPPORTED ON SAID PREHEATER, SAID ENCLOSURE INLET COMMUNICATING WITH THE OUTLET OF SAID PREHEATER, A MEMBER POSITIONED WITHIN SAID ENCLOSURE, SAID ENCLOSURE AND SAID MEMBER SPACED APART TO PROVIDE A NARROW, SUBSTANTIALLY UNIFORM DIAMETER PASSAGE THEREBETWEEN, SAID ENCLOSURE OUTLET COMMUNICATING WITH SAID CHAMBER, AN INSULATED CYLINDER SURROUNDING AND SPACED FROM SAID ENCLOSURE AND SAID PREHEATER, INSULATION SURROUNDING SAID ENCLOSURE AND SAID PREHEATER WITHIN SAID CYLINDER, HEATING MEANS SURROUNDING SAID CYLINDER, AND MEANS FOR MAINTAINING A PRESSURE IN SAID PASSAGE. 